Stabilization of alkyl phenol



Patented Mar. 16, 1954 STABILIZATION OF ALKYL PHENOL COMPOUNDS Jacob J. Menu, Martinez, and Edwin G. Wallace,

Walnut Creek, Calif., assignors to Shell Development Company, Emeryvillc, Calif., a corporation of Delaware No Drawing. Application July 28, 1951, Serial No. 239,184

12 Claims.

This invention relates to the stabilization of alkyl phenol compounds, it being particularly directed to a process for improving the resistance of said compounds against deterioration in color and odor with age.

The alkyl phenols, wherein at least one of the hydrogen atoms attached to the phenyl nucleus is replaced by an alkyl group, are normally lightcolored compounds having a mild odor when freshly prepared. However, many of these compounds take on a definite discoloration when allowed to stand, at the same time acquiring a strong and rather unpleasant odor. This deterioration in quality is particularly manifest in the case of the polyalkyl phenols, many of which, especially the 2,4,6-trialkyl phenols, are employed as oxidation inhibitors in materials where it is important that there shall be no change in the color or odor of the resulting composition.

It is a general object of the present invention to provide a method for improving the resistance of alkyl phenols to deterioration in color and odor with age. A further object is to provide a method of this character which may be effectively employed in the treatment of polyalkyl phenols. The compound 2,6 ditertiarybutyl 4. methyl phenol, though possessing outstanding inhibitor qualities, is especially susceptible to yellowing and odor-development during storage, and it is a particular object to provide a method for improving the colorand odor-stability of this compound. The nature of still other objects of the invention will be apparent from a consideration of the descriptive portion to follow.

It has been discovered that the stability of alkyl The polybasic carboxylic acid or salt employed in stabilizing the alkyl phenol compound can be selected from a wide variety of compounds. Representative stabilizer compounds of this type, any one or more of which can be used in the process of the present invention, are sebacic acid, adipic acid, oxalic acid, citric acid, tartaric acid, diammonium citrate, monosodium citrate, disodium citrate, disodium tartrate, monopotassium adi pate, dipotassium citrate, diammonium tartrate, and monoammonium tartrate. However, a preferred group of compounds for use in stabilizing the alkyl phenols comprises citric acid, tartaric acid, and the alkali metal and ammonium salts of said acids.

The process of the present invention can be practiced with good eifect in the case of any alkyl phenol. Representative starting compounds of this type are o-, mand p-ethyl phenol, p-propyl phenol, p isopropyl phenol, p tertiarybutyl phenol, 2,4-dimethyl phenol, Z-methyI- l-tertiarybutyl phenol, 2-tertiarybutyl-4-methyl phenol, 2- methyl 4 dodecyl phenol, 2,4-ditertiarybuty1 phenol, 2,6-diethyl phenol, 2-methyl-6-tertiarybutyl phenol, 2,4,6trimethyl phenol, 2,6-diethyl- 4-methyl phenol, 2,4,6-triethyl phenol, 2,5-dipropyl-4-methyl phenol, 2,4,6-tripropyl phenol, 2,6-diethyl-4-tertiarybutyl phenol, z-tertiarybutyl-4,6-dimethyl phenol, 2,4,6-tritertiarybutyl phenol, 2,4,6-triisopropyl phenol, 2,4,6-tritertiaryamyl phenol, 2-tertiarybutyl-4,6-ditertiaryamyl phenol, 2-tertiaryamyl-4,6-dimethyl phenol, 2- isopropyl-4,6-dimethyl phenol, 4-methyl- 2,6-ditertiaryamyl phenol and 2,6-ditertiarybutyl-4- tertiaryamyl phenol. However, particularly good results have been obtained in the treatment and resultant stabilization of the polyalkyl phenols, many of which are given above. These polyalkyl phenols are prepared by conventional processes, the usual method being to heat phenol or an alkylated phenol derivative such as 0-, mor p-cresol with an alkene in the presence of an acidic condensing agent such as sulfuric. acid, phosphoric acid, hydrogen chloride or ferric chloride, the alkene attaching to one or more of the carbon atoms of the phenyl nucleus, depending on the reactant proportions employed. The next step in the process is usually to neutralize the reaction mixture with aqueous caustic solution, following which the neutralized product is washed and, if desired, further purified, as by crystallizing the product one or more times from an alcoholic or other liquid solution. The products so obtained are normally light in color and possess little objectionable odor, though many darken rapidly and develop an objectionable odor as they are stored.

The alkyl phenol compounds are stabilized by treatment with a suitable acid or salt in the presence 70f. a solventfor the-.-stabilizer or for both thestabilizer and .-the alkyl'phenol. -When present in the molten condition, the alkyl phenol may itself act as the solvent, though other solvent media such as water, ethyl, methyl, isopropyl and various other alcohols, as well as ethers suchas diethyl ether, methyl ether of diethylene glycol and the like, can be used. --.Thus, the stabilizer compound, in either the presence'on absenceof a solvent, can be added to a fsystemtwhereiniz'the alkyl phenol is present in the liquid condition. Again, a solution of the acid or saltcan be added to the solid alkyl phenol compound. "Theldetails of several available treating methods will be set forth in the examples.

The amount of the stabilizing agent to be employedvis .isusceptible -to some \variation. :Thus, ram'ounts as: small as--0.01 of the acid orwsalt, in terms ofs-the weight :of alkyl' phenol compound present, I have given. good results, though preferadvantage :since therstabilizer can be added to the alkyl phenol 1 icompound E at :the convenience of the r operator; anclirieed 2 not be added oduring 'the-finalLtreating: steps. :iIn somecases-the1latten are practiced :only. after. the slapse of. a Icons'idera-ble period followingithelnriginali'production of the 'alkyl phenolcompound;iduring which period the *1 phenol might :otherwise zhavez deteriorated in color and odor were it not for the stabilization -treatment earlier-practiced.

The process. offithe' present invention is illuse trate'drby the foliowingrexamples EXAMPLE. I

: A. -:A ;quantity: of 1 2,6-ditertiarybutyl-emethyl phenol was :prepared by alkylating s pecresolzwith isobutylene: in"the'. presence of. awmin'or amount of concentrated:sulfuric'acid as. catalyst. The: acid alkylateproducedfin thislimann'er iwas then'neu- .traliz'ed with aqueous'icaustic solution and waterwashed. ":The resulting produ'ct was then? combined'withranrequal weight of. aisoh'entmiaide .up of 85 %:aisopropylialcohokand: 159;; waxer at sot-.10. "-;-'The"-resulfing: solution wasz then' coialed IZOY IOOmTJ- temperature; :thereby erystallizingfi'out thenlkyphenol. These:crystalsvweren'ecovered,

:amount .ofwash solutionxemployed in .each case washed with fresh quantities of the isopropanol solvent, and air dried. As indicated in the table which follows Example IV, the crystalline product so obtained, which was originally white in appearance, and had a mild odor, became progressively darker as it was allowed to age. At the same time, its original mild odor changed in character and grew progressively more unpleasant.

B. Companion operations were conducted under the same conditions as those described in the foregoing paragraph, except that here the neutralized alkylate was washed for a period of 30 minutes not with water, but with a hot (80 C.), 1% aqueous solution of :citric' acid, the

being such that the quantity of stabilizer presaent amounted to 0.3% by weight of the 2,6-diter- "had earlier been washed with citric acid solutiarybutyl-e-methyl phenol. As will be seen froin'='the-"table, the crystalline products which -tiorrrwere :little :changed in either color or odor i'byiithe; storage :period.

tiarybutyl-4-methyl phenol prepared in the manher described in Example I, paragraph A above, wereslur'ried at room temperature with onethird their Weight of-a 0.1% solution of citric aciddn a 'solvent made' up of 85% isoprop'yral- "cohol' and 15% water. Asdnd-icate'd' by the-data presented in the table, 'the'product' recovered from the resulting slurry' had been" completely stabilized.

EX-AMPLE'IH In thisoperation the untreated crystalsprepared as-ciescribed in Example IA-wereiplaced in .a Buchner funnel wheretthey werefwashedz'r'at room temperatures with one-sixth their weight of a 0.1% solution of citric acid in.a*solventscontaining 85% isopropybalcohol and. :15 .water. .As indicated by thedatarpresentedzin theztable, complete protection: against deterioration iini'zthe color- 1 or odor of .the .alkylate'd- I phenoliwas afforded by :the treatment.

EXAMPLE IV In this :'operation the 2,6 ditertiarybutyl-4- methyl phenol :product obtained on neutralizing and Water-Washing the 2,6 -ditertiarybutyl- 4-methyl phenol 1 prepared by treating p-'cresol witlrisobutylene in the presence of sulfuricacid, was'mixed with 20% by'weight of a solventmade upipf' 85% isopropyl alcohol and 15% water; the resulting liquid: being .maintained at Csfor hour. At the end of this period the-organic layerrwas separated and then cooled with stirring; to room temperature, to crystallize out the allsyl phenol. The I crystalline product --'so obtamed was twice washed with alcohol-water'solvent; after which the crystals were air-dried -f or two days. .Asindicatedby'thedata presentin the. table, the i1 crystalline "product obtained=- in this". mannerfrapidlydeteriorated with age.

"companionwoperations conducted under otherwise the same conditions as -described-in the preceding paragraph, various stabilizing agents, =lncludi1'ig 'itric acid; tartaric acid; and diammonium citrate, were introduced alongwith the. alcohol water 1 solvent media'from *which the product: wasicrystallized. As shown the table, eachrof etheset additives fiectively 'sta-bil-ized the product against deterioration in color androdor.

TABLE Stability of 2,6-ditertz'arybut'yl-4-methyl phenol Gardner Color No. of Melt Afterits? Stabilizer Percent 1 1 8 weeks 2 weeks 4 weeks 8 weeks weeks weeks 1 5 12 13 1 1 4 6 l 3 7 12 1 1 1 1 1 3 7 12 1 1 1 l l 2 4 6 1 1 1 2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Percent stabilizer employed, based on weight of 2, 6-diterttary-butylA-methyl phenol present.

7 On the Gardner Color Scale, No. 1 corresponds to a nearly water-white liquid.

N0. 5 is a very pale yellow, and No. is a deep yellow. This scale is defined in the reference work by Gardner and Sward, Physical and Chemical Examination, Paints, page 9. Published by Henry A. Gardner Laboratory, Inc.,

The claimed invention is:

1. The method for improving the colorand odor-stability of an alkyl phenol having an alkyl group of at least two carbon atoms, comprising treating said alkyl phenol with at least one stabilizer compound selected from the group consisting of the polybasic carboxylic acids and the salts of said acids, the amount of said treating agent being 0.01% to about 1% by weight of said alkyl phenol.

2. The method of claim 1 wherein the treatment is effected in the presence of a solvent for said stabilizer compound.

3. The method of claim 1 wherein the alkyl phenol is a polyalkyl phenol.

4. The method of claim 1 wherein the alkyl phenol is 2,6-ditertiarybutyl-4-methyl phenol.

5. The method of claim 1 wherein the alkyl phenol is 2,6-ditertiarybutyl-4-methyl phenol and the stabilizer compound is citric acid.

6. The method of claim 1 wherein the alkyl phenol is 2,6-ditertiarybutyl-4-methyl phenol and the stabilizer compound is tartaric acid.

7. The method for improving the color and odor-stability of an alkyl phenol having an alkyl group of at least two carbon atoms, comprising crystallizing said alkyl phenol from a solution containing 0.01% to about 1%, based on the weight of said alkyl phenol, of a polybasic carboxylic acid.

8. The method of claim 7 wherein a ditertiary varnishes Lacquers, Colors," 1950 ed., 4723 Elin sa,

Bethesda, Md.

alkyl-methyl phenol is crystallized from an aqueous isopropyl alcohol solution of an aliphatic dicarboxylic acid.

9. The method for improving the colorand odor-stability of an alkyl phenol having an alkyl group of at least two carbon atoms, comprising treating said alkyl phenol with 0.01% to about 1% by weight of said alkyl phenol of a, hydroxy polybasic carboxylic acid.

10. The method for improving the colorand odor-stability of an alkyl phenol having an alkyl group of at least twocarbon atoms, comprising treating said alkyl phenol with 0.01% to about 1% by weight of said alkyl phenol of a polybasie carboxylic acid salt.

11. The method of claim 10 wherein the polybasic carboxylic acid salt is an alkali metal salt.

12. The method of claim 10 wherein the polybasic carboxylic acid salt is an ammonium salt.

JACOB J. MENN. EDWIN G. WALLACE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,095,801 Engel Oct. 12, 1937 2,297,588 Stevens et al Sept. 29, 1942 2,415,069 Arvin et al. Feb. 4, 1947 2,493,781 Schneider et a1 Jan. 10, 1950 2,559,594 Caplan July 10, 1951 

1. THE METHOD FOR IMPROVING THE COLOR- AND ODOR-STABILITY OF AN ALKYL PHENOL HAVING AN ALKYL GROUP OF AT LEAST TWO CARBON ATOMS, COMPRISING TREATING SAID ALKYL PHENOL WITH AT LEAST ONE STABILIZER COMPOUND SELECTED FROM THE GROUP CONSISTING OF THE POLYBASIC CARBOXYLIC ACIDS AND THE SALTS OF SAID ACIDS, THE AMOUNT OF SAID TREATING AGENT BEING 0.01% TO ABOUT 1% BY WEIGHT OF SAID ALKYL PHENOL. 